Top quark nabbed

Published: Saturday 15 April 1995

THE elusive top quark has at last been nabbed: 2 competing teams of quark-hunters at the Fermi National Accelerator Laboratory (Fermilab) at Illinois, usa, caught the last undiscovered quark of the sextet -- bottom, up, down, strange and truth -- theoretically outlined in the '60s as the 6 fundamental particles constituting matter.

Says V Singh, director of the Bombay-based Tata Institute of Fundamental Research, one of the collaborating institutions in the experiment, "The eagerly-awaited discovery provides the final piece of evidence to support the standard model -- the central theory in physics that describes fundamental particles and the forces that act on them."

Last April, one of the teams had recorded 12 possible top quarks. By end of the last month, the team had 39 candidates, enough to calculate the mass of the particle. The team says that the chance that the much-awaited signals were produced by some random fluctuation in the accelerator are less than 1 in a million.

The discovery has dispelled the cloud of uncertainty that had been hanging over the measurements recorded at Fermilab last year using an instrument called the Collider Detector, or the d-zero detector.

The Fermilab detector fires protons and antiprotons in opposite directions around a 6.3 km-long torus-like ring. The collision between the 2 particles creates a shower of debris of subatomic particles including, occasionally, a top quark.

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